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Cell-specific effects of RAS oncogene and protein kinase C agonist TPA on P-glycoprotein function
T P Stromskaya1, I A Grigorian, V S Ossovskaya
1Institute of Cancerogenesis, Cancer Research Center, Moscow, Russian Federation.
Abstract:
We compared the influence of exogenous N-ras oncogene and treatment with PKC agonist 12-O-tetradecanoylphorbol-13-acetate (TPA) on P-glycoprotein (Pgp) function in various human, rat and dog cell lines. Two approaches were used: (a) flow cytometry analysis of Rhodamine 123 (Rh123) exclusion; and (b) sensitivity to cytotoxic action of colchicine. We have found that in Rat1 fibroblasts, rat IAR2 epithelial cells and rat McA RH 7777 (hepatoma), ras activates Pgp function, while in MDCK (dog kidney), K562 (human chronic myelogenous leukaemia) and LIM1215 (human colon carcinoma) cells it either has no effect or even acts in opposite direction. TPA-induced Pgp function shows dissimilar pattern of cell specificity. It is assumed that PKC and ras oncogene regulate mdr1 gene expression through at least partially distinct signalling pathways.
Insights
The N-ras oncogene activates P-glycoprotein (Pgp) function in some cells, but not others. Protein kinase C (PKC) activation also shows cell-specific effects on Pgp, suggesting distinct signaling pathways.
Area of Science:
- Cell Biology
- Molecular Biology
- Oncology
Background:
- P-glycoprotein (Pgp) is a key efflux pump involved in multidrug resistance.
- The N-ras oncogene and protein kinase C (PKC) are implicated in cellular signaling pathways that can influence Pgp function.
- Understanding the regulation of Pgp is crucial for overcoming drug resistance in cancer therapy.
Purpose of the Study:
- To investigate the impact of the N-ras oncogene and PKC agonist TPA on Pgp function across diverse cell lines.
- To determine if ras oncogene and TPA exhibit similar or distinct patterns of Pgp modulation.
- To explore the underlying signaling mechanisms involved in ras and PKC-mediated Pgp regulation.
Main Methods:
- Utilized flow cytometry to analyze Rhodamine 123 (Rh123) exclusion as a measure of Pgp activity.
- Assessed cellular sensitivity to the cytotoxic agent colchicine to evaluate Pgp function.
- Compared the effects of exogenous N-ras oncogene expression and TPA treatment in human, rat, and dog cell lines.
Main Results:
- N-ras oncogene activated Pgp function in Rat1 fibroblasts, IAR2 epithelial cells, and McA RH 7777 hepatoma cells.
- N-ras had no effect or an inhibitory effect on Pgp in MDCK kidney, K562 leukemia, and LIM1215 colon carcinoma cells.
- TPA-induced Pgp function displayed a different cell-specific pattern compared to ras activation.
Conclusions:
- Ras oncogene and PKC signaling pathways differentially regulate Pgp function depending on the cell type.
- The findings suggest that ras and PKC modulate mdr1 gene expression via at least partially distinct signaling routes.
- These distinct regulatory mechanisms highlight the complexity of Pgp control and its implications for multidrug resistance.